Switchgear is the aggregate of switching devices for a power or transforming station or for electric motor control. A bus is provided, to which are connected the generator (source) and the feeder lines (load). Both generators and feeders are connected to the bus through automatic circuit breakers (interrupters) and disconnecting switches.
Switchgear patents date back as far as U.S. Pat. No. 1,768,535 issued Jul. 1, 1930 which describes an electric switch that is mounted on wheels to be moved into and out of contact with circuit leads such that the movable terminals are caused automatically to be connected electrically with fixed circuit leads when the movable switch is in the inserted position and automatically disconnect when the switch is withdrawn from the stationary enclosing cell.
The electric switch includes a switch lock such that the switch cannot be withdrawn when the locking bar is in its lower most position. When the locking bar is raised, the switch can be withdrawn. The raising means can be a bell crank lever coupled with an operating rod that extends through the cover plate. There is also provided a means (switch operating mechanism) to prevent the unlocking when the switch is closed. The switch operating mechanism can include an operating shaft adapted to be rotated in one direction when the switch is opened and an opposite direction when the switch is closed. The combination of the bell crank lever and switch operating mechanism function such that when the switch is not fully inserted, the operating mechanism cannot close the switch and when the operating mechanism closes the switch, it automatically operates to move the locking bar to lock the switch in position.
U.S. Pat. No. 2,443,669 issued Jun. 22, 1948 discloses a switchgear apparatus that includes a drawout mechanism for securing the removable switchgear in either of its extreme positions or intermediate position between its limits of travel. And to interlock the drawout mechanism and the operating mechanism (actuate by handle disposed in an opening provided in the door) for the removable circuit breaker to prevent improper operation.
As stated in U.S. Pat. No. 2,298,828 issued on Oct. 13, 1942, “[i]n metal-enclosed switchgear of the drawout type, the conventional arrangement comprises a stationary metal housing within which bus bars, cable leads, and accessory apparatus are disposed and a removable unit comprising a circuit breaker which is connected to the busses and incoming and outgoing leads in the operating position of the unit. In this position, so-called primary disconnecting contacts include contacts connected to the buses and incoming or outgoing leads fixedly mounted with respect to the stationary housing and coacting movable contacts carried by the removable unit are in engagement.
The apparatus is also provided with suitable interlocking means generally arranged so that it is impossible to insert or withdraw the removable unit or break connected at the primary disconnecting contacts without first tripping the circuit breaker, and insuring that the circuit breaker is open both when the unit is moved out of and into operative position”. The electric switchgear also includes a rack out mechanism, a mechanical interlock to prevent movement of the removable unit with respect to the stationary housing; a trip knob and locking device for tripping the circuit breaker device.
U.S. Pat. No. 2,388,934 issued Nov. 13, 1945 teaches a circuit breaker control mechanism for circuit breakers that are housed in compartments with a door. The CB is mounted on a movable frame or truck. The movable frame carries moving contacts that engage stationary contacts at the rear of the stationary frame for connecting the circuit breakers to the buses and contacts at the rear for control purposes. The patent describes rotating the latch rod to trip all three poles of the circuit breaker, causing them to move to their movable contact arm to the open position by depressing push button provided on the door for manually tripping the circuit breakers when the door is closed. This '934 patent is a divisional of U.S. Pat. No. 2,129,723 filed on Sep. 29, 1936 which issued Sep. 13, 1938.
An early draw out fused switch gear assembly is taught in U.S. Pat. No. 3,274,356. The assembly is adapted to be removably engageable with fixed electrical connectors from a electrical source. Another early patent, U.S. Pat. No. 2,982,827, describes an interlocking mechanism for use with a slidably mounted electrical draw out unit for forward and backward movement between an advanced and a retracted position in which movable contacts of the high voltage supply source that mate with stationary source.
U.S. Pat. No. 3,842,321 issued to Caton on Oct. 15, 1974 clearly describes the conventional high voltage switchgear having a primary supply switching means and operating mechanism, usually in conjunction with a circuit breaker, being mounted partly internal and partly external to the enclosure of a movable housing, with the current inlet and outlet conductors mounted in a stationary housing, which may also contain other electrical equipment, for example bus bars, cable box and instrument transformers.
The two housings can have isolating means such as mating plug and socket contacts for transmitting the primary supply of high voltage electricity through the switching means, the contacts being made or broken according to the relative position of the two housings. With the contacts made, switching is effected by operation of the switching means on the movable housing. Apart from the primary high voltage supply such switchgear includes a number of secondary circuits, generally low voltage control and indicator circuits, which may be fed from current and voltage transformers in the stationary housing and controlled by switches operated in accordance with the state of the primary switching means. When a circuit breaker is incorporated this is usually tripped by energiation of the circuit breaker shunt trip coil by a protective relay, the protective relay energized by an instrument transformer.
In conventional systems the power supplies for secondary circuits are taken from means in the stationary housing, but the elements of the secondary circuit responsive to such power, e.g. trip coils, auxiliary switches and electrical interlocks, are located in the movable housing.
U.S. Pat. No. 5,481,075 issued on Jan. 2, 1996 to Kleinecke et al. discloses a compact motor control (switchgear) with an improved arrangement for disconnecting and withdrawing a drawout unit that includes windows (not shown) through which blades can be viewed to visibly confirm that the isolation switch is open and that the blades are grounded prior to maintenance. U.S. Pat. No. 4,206,329 issued Jun. 30, 1980 shows windows in FIG. 1 for viewing in conjunction with a handle indicator that functions as both a drawout latch pin release and as an indicator that switch operating mechanism is uncoupled.
U.S. Pat. No. 7,277,294 issued to Carlson on Oct. 2, 2007 describes a contactor draw out pan that has a movable frame and a stationary frame which carries the electrical components for an electrical feeder circuit and has input terminals for the incoming electrical power and output terminals for delivering electrical power to equipment operating on the feeder circuit. The movable frame carries the contactors. A disconnect mechanism locks the movable frame relative the stationary frame and provides a primary mechanical means for disengaging electrical current flow through the apparatus. While the contactor draw out pan provides access for repairs, the operator is required to stand in front of the device to mechanically disengage the electrical current flowing between the input and output terminal before the pan can be drawn out for repairs.
Other prior art patents include, U.S. Pat. No. 2,218,555 issued to Rossman on Oct. 22, 1940; U.S. Pat. No. 2,554,510 issued to Spicer on May 29, 1951; U.S. Pat. No. 3,716,684 issued to McMillen on Feb. 13, 1073; U.S. Pat. No. 3,842,321 issued to Caton on Oct. 15, 1974; U.S. Pat. No. 3,896,353 issued to Burton on Jul. 22, 1975; U.S. Pat. Nos. 3,923,197 and 3,983,460 issued to Kuhn on Dec. 12, 1975 and Sep. 28, 1976, respectively; U.S. Pat. No. 3,991,291 issued to McGuffie on Nov. 9, 1976; and U.S. Pat. Nos. 4,002,864; 4,002,865 both issued to Kuhn on Jan. 11, 1977, and U.S. Pat. No. 4,017,698 issued to Kuhn on Apr. 12, 1977; U.S. Pat. No. 4,482,936 issued to Saito Nov. 13, 1984; U.S. Pat. No. 6,127,742 issued Oct. 3, 2000 describes a draw-out electrical switchgear apparatus; and U.S. Pat. No. 6,031,192 issued Feb. 29, 2000 describes a draw out circuit breaker with disconnect position interlock mechanism.
High voltage switching equipment commonly includes a variety of safety features such as barriers between phases to avoid arching between phases and a viewing window to provide line-of-sight to internal components so that a user can monitor the connection status of the switching components when the switching equipment is fully installed in a long wall enclosure.
A power center is a multi-compartment steel enclosure with a bus system to distribute electrical power, on a common bus system, to individual switching equipment units mountable within the compartments. The individual switching equipment are commonly referred to as “buckets” and are typically constructed to be removable, pull-out units that have, or are installed behind, individual sealed doors on the power center enclosure. These buckets can contain various switching control and motor protection components such as motor controls, starters, contactor assemblies, overload relays, circuit breakers, motor circuit protectors, various disconnects, and similar devices for electric motors. The buckets connect to the supply power lines of the power center and conduct supply power to the line side of the switching equipment, for operation of motors. Power centers are most often used in the underground mining industry, which uses high power electrical motors, pumps, and other loads.
A problem with prior art switchgear, circuit interrupters and contactor equipment is the size and weight of the draw out cell/contactor pan also referred to as a contactor bucket. Removal of the prior art contactor buckets from the stationary rack requires multiple screws to be removed, and because of the weight, required two or more operators to remove the draw out cell from the stationary rack or longwall power distribution unit.
To solve the problems associated with the prior art draw out cells, the methods, systems and apparatus of the present invention includes safety features such as a dead front panel, a motorized racking mechanism that can be automatically or remotely operated, insulated internal components to reduce complexity, decrease size and reduce weight while increasing safety. A dead front panel is a panel where all energized components are insulated to protect personnel from electrocution.